Controlled/Living Cationic Polymerization of p-Methoxystyrene in Solution and Aqueous Dispersion Using Tris(pentafluorophenyl)borane as a Lewis Acid: Acetonitrile Does the Job

Abstract

The living cationic polymerization of p-methoxystyrene using the 1-(4-methoxyphenyl)ethanol/B(C6F5)3 initiating system in solution and in aqueous dispersion is reported. Solution experiments first showed that the molar mass of the obtained polymers increases in direct proportion to the monomer conversion and the molar mass distribution stays narrow in the course of the polymerization (Mw/Mn ∼ 1.2). The living nature of the growing chains was confirmed by sequential monomer addition experiments, although matrix-assisted laser desorption ionization time-of-flight mass spectroscopy (MALDI-TOF-MS) revealed some hydroxyl elimination under monomer-starved conditions. Aqueous suspension polymerization of p-methoxystyrene using the same initiating system did not show a good control of molar masses, since after polymerization has proceeded at the interface up to critical DP, oligomers terminated by water penetrate inside the particles where they stop propagating. This limitation was leveled off for the first time by polymerizing p-methoxystyrene in an aqueous dispersion, i.e., in a mixture of H2O:CH3CN 3:2 (v/v). Under these conditions, the hydroxyl-terminated poly(p-methoxystyrene)s can be reactivated by B(C6F5)3 located inside the particles to reinitiate the polymerization; molar masses thus increase with conversion, up to 3000 g mol-1, and exhibit a narrow molar mass distribution (Mw/Mn ∼ 1.3) and an almost pure hydroxylated functionality.